Brief Description Of The Prior Art
In the refining of petroleum, and particularly, in catalytic cracking of various hydrocarbon stocks to yield valuable lower boiling hydrocarbons, such as gasoline, the catalyst particles are frequently entrained in the vapor product from the cracking zone going to the distillation zone. It is desirable in many instances to separate the catalyst fines (ash) from the slurry oil which will usually be the bottoms product from a distillation carried out on the product from the catalytic cracker. In the separation of catalyst fines from a fluidized catalytic cracker slurry oil, several schemes have heretofore been used, such as settling or decantation, centrifugal separation, and filtration, but these do not generally remove the catalyst to as low a level as desired, are high maintenance items and are difficult to operate. In some instances, the expense makes the method of catalyst removal prohibitive.
A number of prior art patents describe various catalyst removal techniques and specifically describe the removal of catalyst fines (variously called spent catalyst or ash) from the heavy product of catalytic cracking. Usually, the liquid product resulting from catalytic cracking is charged to a fractionation column and the bottoms from that column is referred to as slurry oil. It contains most of the catalyst fines used in the catalytic cracking process, and generally is high in aromatics or refractory compounds which make it less than optimum for recycling to the catalytic cracking process. On the other hand, with the fines removed from the slurry oil, the resulting clarified oil is an excellent charge stock for carbon black production, or for use as a fuel oil. To the extent, however, that catalyst fines remain in the clarified oil the value of the carbon black product is decreased.
U.S. Pat. No. 4,345,991 to Stegelman, assigned to Phillips Petroleum Company, describes a process for separating catalyst fines from slurry oil resulting from a catalytic cracking operation. It is acknowledged that by such removal, the clarified oil resulting is a good charge stock for the production of carbon black. In this instance, the patentee proposes to remove the catalyst fines by filtration, followed by back flushing the filter with a suitable catalytic cracker feedstock so as to pick up the fines and recreate a charge stock for the catalytic cracker having the fines entrained therein. Hydrocarbon material used for back flushing the filter may be a topped oil, or a vacuum reduced crude oil. The filter used can be any of various types known to the art.
In U.S. Pat. No. 3,928,158, a process for cleaning up the slurry oil by removal of catalyst particles therefrom is described. An electrofilter is used for the removal of catalyst particles.
In U.S. Pat. No. 3,617,503 to Rogers, a process is disclosed for conversion of asphaltene-containing hydrocarbonaceous charge stock into lower boiling hydrocarbon products. The process involves the use of a catalyst-containing slurry. The catalyst particles are separated from the reaction product by using a foam chamber and a foam breaker.
In U.S. Pat. 3,591,485 to Mason, Jr., assigned to Phillips Petroleum Company, a part of the catalyst-containing slurry from a catalytic cracker is subjected to solvent extraction to remove the aromatics from the slurry oil. This extraction leaves the catalyst fines in the predominantly paraffinic raffinate stream which remains after the extraction. The extracted aromatics are used as a carbon black feedstock. The paraffinic raffinate containing the catalyst fines can be recycled to the catalytic cracker.
In U.S. Pat. No. 4,309,273 to Washer and assigned to Phillips Petroleum Company, catalyst fines are cyclonically removed from slurry oil, and the clarified product can then be used in the manufacture of carbon black.
Steenborg U.S. Pat. No. 3,600,300 describes methods of separating catalyst slurries from hydrocarbon streams, including filtration, settling tanks and centrifugation and also describes washing the separated catalyst particles with methylnaphthalene to remove residual hydrocarbon from the catalyst sludge.
U.S. Pat. No. 3,489,673 to Stine et al describes a method of separating catalyst fines from a slurry oil from a catalytic cracking process by settling, and also by the use of a cyclone. The clarified oil remaining is described as useful as a fuel oil.